There are more than 40,000 species of spiders, almost
all of them venomous, but only a few are known to produce venom
that is toxic to humans.

Thanks to antivenin and good medical care,
deaths from spider bites have steeply declined since the
1950s, according to records kept by national poison control
centers. Changes in how people live have helped, too. For
example, in the United States, the switch to indoor plumbing
sharply cut black widow bites. That's because men using outhouses
were often bitten on the penis or scrotum, where the thin skin
and abundant blood vessels meant venom quickly entered the body,
a doctor reported in 1942 in the Annals of
Surgery.

"People think every spider bite is deadly, but the ones you hear
about are the tragic ones," said Richard Vetter, an arachnologist
and retired research associate at the University of California,
Riverside. "It's like car accidents. Most car accidents are not
remarkable, and most spider bites are not that big of a deal."
[ Creepy,
Crawly & Incredible: Photos of Spiders ]

Vetter devoted several decades of his career to publishing
reliable information on spiders for non-experts. He
recently addressed the mistaken beliefs surrounding the world's
deadliest spiders in an essay published on
The Conversation. Here, Live Science has edited and condensed
an interview with Vetter on spider myths and misconceptions.

Funnel web spiders (Atraxrobustus and
others)

Australia's funnel web spiders are probably the most toxic
spiders to humans. Their bites can kill adults in 24 hours
without treatment and are even more lethal in children. Symptoms
typically start in less than 10 minutes. "They've got a wallop,"
Vetter said.

The intensely painful bites jam the body's communication network,
including signals that control the heart and lungs. However, no
one has died from a funnel web spider bite since 1981, when
antivenin was developed,
an Australian study reported in 2005. The glossy black
spiders live within the Sydney urban area and along the
southeastern Australia coast.

Brazilian wandering spider (Phoneutria)

Three species of Phoneutria spiders found in Brazil are
potentially deadly, but according to Vetter, the spiders are
rarely found outside the country, despite stories of the
creatures
infesting banana shipments. Rather, the hairy, red-faced
banana spiders are often victims of mistaken identity, he said.
That's because the harmless Cupiennius species, found in
Mexico and Central America, strongly resembles its lethal
relative. This nonlethal spider sometimes hitches a ride in
bananas bound for export, scaring workers who open the shipments.
Vetter has documented several mix-ups by spider experts (who
weren't familiar with either species) in a study published
September 2014 in the Journal of
Medical Entomology.

The deadly Phoneutrias rarely leave Brazil, Vetter said.
The most dangerous and toxic species, P. fera, is only
found deep in the rainforest (far from banana plantations). Two
other Phoneutria species live in eastern Brazil, and
their bites cause mild to no symptoms in 80 percent of adults.

Widow spiders (Latrodectus)

Widow spiders are a global group, with 32 species recognized
worldwide. In the United States, people rightly feared black
widow bites before antivenin was developed. About 5 percent of
bites were fatal, but now, black widow deaths are rare. Between
2000 and 2008, there were more than 23,000 black widow bites
reported in 47 states and no deaths, according to statistics
kept by the American Association of Poison Control
Centers.

Brown recluse spiders (Loxosceles)

Brown
recluse spiders are another globetrotting spider species
native to North America. Most commonly found in the Southeast and
Midwest, their bites are rarely fatal. And only about 10 percent
of recluse bites become skins lesions because the venom destroys
the capillaries that supply blood and oxygen to skin cells.
Without blood, the skin dies.

Beginning in the 1990s, physicians started blaming brown recluse
spiders more often when patients turned up with mysterious
festering sores. The misdiagnoses emerged at the same time as
community-associated Methicillin-resistant
Staphylococcus aureus (MRSA), a strain of staph
bacteria that is resistant to antibiotics. (Cancer and several
other diseases can also cause skin problems that resemble spider
bites.) Many of these cases were in states where brown recluse
spiders are rarely found.

Vetter first showed that medical diagnoses of brown recluse bites
greatly outnumbered the actual number of spiders in a 2003 study
published in the journal Toxicon.
In the decade since, the medical mistakes have dropped, Vetter
told Live Science. This shift is partly due to growing awareness
of MRSA among physicians, he said.

"I used to get 30 to 50 emails a year about brown recluse bites,"
Vetter said. "It's dropped down to 1 or 2 a year."

However, people can die from encounters with a brown recluse
because there is no antivenin available in the United States. In
less than 10 percent of cases, the venom triggers a devastating
and massive breakdown of red blood cells. This systemic reaction
is more common in children, and seems to vary by
Loxosceles spider species, a 2011
Lancet study reported.

An antivenin is available in Brazil for a recluse spider species,
but its production causes the early death of thousands of horses
and spiders. Research groups are trying to develop a synthetic
alternative.